In the lithium ion secondary battery, safety and high temperature storage properties, as well as the cycle life at room temperature and at high temperatures, are essential to the application of the battery. The factors that most affect these elements are the characteristics of the cathode active materials and anode active materials. Recently, there has been much development in the field of anode active materials, while there are many problems to be improved upon in the field of cathode active materials. In particular, safety and high temperature storage properties of a battery depend on cathode active materials. As standard cathode active materials for the above lithium ion secondary battery, LiCoO2, LiNiO2, and LiMn2O4 have been known. Although LiNiO2 has the highest discharge capacity, problems arise in applying this material to practical use due to difficulties in synthesis and thermal safety. LiMn2O4 is relatively low in price and does not harm the environment, but cannot be used alone, since it has a small specific capacity. LiCoO2 has been used commercially for it has a high battery voltage and excellent electrode characteristics. However, it has poor storage properties at high temperatures. In order to resolve these problems, much research has been performed. According to Japanese Unexamined Patent Publication No. Hei 11-317230, the cycle life and safety of a battery have been enhanced by a metal oxide coating. In the LiNiO2 system, structural safety is improved by use of several dopants. In addition, safety of the battery is improved by improving thermal safety. Safety and cycle life of the battery are also improved by adding an additive to an electrolyte. However, such improvements do not affect storage properties and cycle life at high temperatures.